1. Field of the Invention
The present invention relates to a directional control valve and to a valve assembly employing a plurality of individual directional control valves which are connected together in a linked construction whereby a desired number of individual valves can be linked together without using a manifold base, subplates and the like.
2. Description of the Related Art
There have been previously known valve structures in which a plurality of directional control valves are installed on an integrated manifold base having a supply passage and an exhaust passage for a pressurized fluid, or wherein the directional control valves are respectively installed on a subplate having a supply passage and an exhaust passage for a fluid, whereby the valves are capable of mutual communication with each other in a linking manner in order to collectively supply and exhaust a pressurized fluid to the plurality of directional control valves.
However, when a plurality of directional control valves are installed on a manifold base or subplates, as described above, problems arise in that time and labor are required for installation of the directional control valves on the manifold base or subplates, and the manifold or subplates require the directional control valves to occupy a large space and height. Further, difficulties arise in that it becomes necessary to prepare the manifold or subplates taking into account the number of directional control valves which are to be linked together, so that the manifold or subplates correspond to the length of the so-linked directional control valves. As a result, the number of required parts increases, and an inconvenience arises in that production cost for the directional control valves and the valve assembly thereof increases.
In order to solve such problems, there has been proposed a valve assembly in which a plurality of directional control valves are stacked together, and in which supply ports and exhaust ports to be mutually communicated by such a linking construction are connected by bolts and nuts passing through connecting holes which extend through the directional control valves.
Such directional control valves and valve assemblies have advantages in that time and labor for installing the directional control valves are decreased, and the space and height required for installation can be kept small, because neither a manifold nor subplate is used.
Such a known stacking-type directional control valve is shown in FIG. 1. In this directional control valve, a valve hole 2 is defined at a central portion in a longitudinal direction of a main valve body 1, and a valve member 3 is displaceably provided in the valve hole 2. A solenoid 4 is provided at one end side of the main valve body 1, whereby an ON-OFF operation of the solenoid 4 allows the aforementioned valve member 3 to be displaced to the right or left, as illustrated in the figure. Output ports A, B are provided on an upper surface of the main valve body 1, and a supply port P and exhaust ports EA, EB are defined perpendicularly to the valve member 3 on a side surface of the main valve body 1. Incidentally, in the figure, reference numerals 5, 6 indicate holes for linking together a large number of such directional control valves by inserting bolts.
However, occurrence of a different problem occurs in such a directional control valve in that a pressurized fluid, which flows through the supply port P and the exhaust ports EA, EB penetrating through the main valve body 1, flows across the valve hole 2, so that the pressurized fluid comes into contact with a lubricant such as grease or the like applied to the valve member 3, and the lubricant is splashed about by the fluid. Thus, the durability of the directional control valve itself deteriorates due to a deficiency in lubrication of the valve member 3. Further, when an individual directional control valve must be exchanged or repaired due to failure or breakage, it is impossible to remove a single directional control valve from the valve assembly unless the valve assembly is completely disassembled, so that maintenance of the valve assembly is troublesome.